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Viper 422


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#1 renfield sonia

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Posted 11 January 2011 - 05:34 AM

Hi, I'm going to shoot a low budget feature film using a viper camera and a panasonic p2 AVCINTRA 100 recorder. As it's recording in 422 HD I'm thinking about the filmstream signal that the camera is going to feed to the recorder, mainly concerned about the colour correction process.
Shooting with 444 RGB filmstream (RAW like uncompressed image) output is easy as you have a lot of range to correct, at first the greenish cast of the filmstream mode, and then to set the blacks and whites proper values. Even if we used magenta filters I guess that this time we'll be much more limitated by this colour mode... anyone has any experience about colour latitude in such a case? Do we have to be more conservative in contrast ranges? My main concert is the green cast of the sensor as sometimes it'll demand for a strong correction just to begin with... I'm also concerned about the gamma curve (filmstream) that is similar to log curves, so to increase latitude, that leads to a low contrast image that needs to be corrected in post: by rising up the white point for example, it's just a guess because I'm not a colorist (I'll be the DIT of the project) but when I'm making colour previews using captures (DPX images from cinetal monitor) and using photoshop, strong contrast corrections give uneven histograms... so I guess that many tones are missing... Is this a real possibility?
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#2 Phil Rhodes

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Posted 11 January 2011 - 06:17 AM

Viper in 4:2:2 "videostream" is pretty clippy and nasty, to the point where I'd say if you have to do that there are better cameras to use. You'll have vastly more freedom to grade if you shoot in 4:4:4 "filmstream", but as you say, you need to ensure that your postproduction chain can handle it.

I think people did tests with magenta filters and discovered that all you actually do with that technique is make all the colour channels clip at different points, which can cause strangely tinted highlights. Run your own tests.

P
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#3 renfield sonia

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Posted 15 January 2011 - 07:10 AM

The philosophy of magenta filters is just about colour clipping, as the viper seems to be much more sensitive to green spectrum of light (about one stop) this channel clips sooner than the two others hence giving a magenta cast to highlights. By correcting this difference you allow the clipping point to decrease about 1 stop and balancing the three channels. You got at the end more exposure latitude and a wider range for color correction (you don't have to boost up the blues or reds to match the green channel).
I've shot a little test with the viper and didn't see any difference between the two modes, wich would be reasonable due to the monitoring limitations, but want to perform a more exact test mainly concerning the exposure latitude (which is very interesting)
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